High surface area layered double hydroxides

ABSTRACT

Layered double hydroxides having a high surface area (at least 125 m 2 /g) and the formula (I) 
       [M z+   1-x M′ y+   x (OH) 2 ] a+ (X n- ) a/n   +   b H 2 O. c (AMO-solvent)  (I)
 
     wherein M and M′ are different and each is a charged metal cation (and must be present), z=1 or 2; y=3 or 4, 0&lt;x&lt;0.9, b is 0 to 10, c=0 to 10, X is an anion, n is the charge on the anion, and a=z(1−x)+xy−2; AMO-solvent is aqueous miscible organic solvent, may be prepared by a method which comprises
     a) precipitating a layered double hydroxide having the formula   

       [M z+   1-x M′ y+   x (OH) 2 ] a+ (X n- ) a/n   +   b H 2 O
         wherein M, M′, z, y, x, a, b and X are as defined above from a solution containing the cations of the metals M and M′ and the anion X n- ;       b) ageing the layered double hydroxide precipitate obtained in step a) in the original solution;   c) collecting, then washing the layered double hydroxide precipitate;   d) dispersing the wet layered double hydroxide in an AMO solvent so as to produce a slurry of the layered double hydroxide in the solvent;   e) maintaining the dispersion obtained in step d); and   f) recovering and drying the layered double hydroxide.   

     The high surface area products have low particle size and are particularly suitable for use as catalysts, catalyst supports, sorbents and coatings.

The present invention relates to high surface area layered doublehydroxides (LDHs) and to methods of making them.

Layered double hydroxides (LDHs) are a class of compounds which comprisetwo metal cations and have a layered structure. A review of LDHs isprovided in Structure and Bonding; Vol 119, 2005 Layered DoubleHydroxides ed. X Duan and D. G. Evans. The hydrotalcites, perhaps themost well-known examples of LDHs, have been studied for many years. LDHscan intercalate anions between the layers of the structure. WO 99/24139discloses use of LDHs to separate anions including aromatic andaliphatic anions.

Owing to the relatively high surface charge and hydrophilic propertiesof LDHs, the particles or crystallites of conventionally synthesisedLDHs are generally highly aggregated. The result of this is that, whenproduced, LDHs aggregate to form “stone-like”, non-porous bodies withlarge particle sizes of up to several hundred microns and low specificsurface area of generally 5 to 15 m²/g (as disclosed for example in Wangat al Catal. Today 2011, 164, 198). Reports by e.g. Adachi-Pagano at al(Chem. Common. 2000, 91) of relatively high surface area LDHs havespecific surface areas no higher than 5 to 120 m²/g.

In certain applications (for example adsorbents or catalyst supports),it would also be advantageous to provide LDHs with higher surface areasthan currently known. Relatively high surface areas would lead to agreater number of active sites and facilitate mass transport from thesurface to bulk.

We have found that high surface area LDHs can be prepared by a simplemethod in a cost effective way involving fewer operational steps andusing smaller quantities of organic solvents compared to other knownmethods. This simple method will be more amenable to large scaleproduction than previous known methods.

Accordingly, the present invention provides a method of preparing alayered double hydroxide having a specific surface area of at least 125m²/g and having the formula:

[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(n-))_(a/n) ⁺bH₂O.c(AMO-solvent)  (I)

wherein M and M′ are different and each is a charged metal cation (andmust be present), z=1 or 2; y=3 or 4, 0<x<0.9, b is 0 to 10, c=0 to 10,X is an anion, n is the charge on the anion, and a=z(1−x)+xy−2;AMO-solvent is aqueous miscible organic solvent, which method comprises

-   a) precipitating a layered double hydroxide having the formula

[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(n-))_(a/n) .bH₂O

-   -   wherein M, M′, z, y, x, a, b and X are as defined above from a        solution containing the cations of the metals M and M′ and the        anion X^(n-);

-   b) aging the layered double hydroxide precipitate obtained in    step a) in the original solution;

-   c) collecting, then washing the layered double hydroxide    precipitate;

-   d) dispersing the wet layered double hydroxide in an AMO solvent so    as to produce a slurry of the layered double hydroxide in the    solvent;

-   e) maintaining the dispersion obtained in step d); and

-   f) recovering and drying the layered double hydroxide.

In step a) of the method of the invention, the layered double hydroxidewill typically be produced by adding an aqueous precursor solutioncontaining ions of the metals M and M′ into a solution containing theanion X which may additionally contain NaOH or to which NaOH solutionmay be added separately in order to adjust the pH of the solution to apredetermined value, typically greater than 7, preferably greater than9, more preferably 10-12. It is, according to a preferred embodiment,desirable to add the metal precursor solution to the anion solutionrapidly with vigorous stirring since this promotes rapid nucleation ofthe LDH. We have found that this rapid addition and quickco-precipitation stage causes the LDH colloid formed to have a smallerand thinner particle size. The LDH is subjected to ageing in theoriginal reaction solution and, preferably, the solution containing theprecipitated LDH will be aged for less than 24 hours, preferably lessthan 16 hours and more preferably less than 3 hours. In step c) of themethod, the precipitated layered double hydroxide is collected and thenwashed. Typically, the precipitate is collected by filtration. Aftercollection, the precipitate is washed until the washing solution has apH which is substantially neutral, for example pH 7±0.5. Washing istypically carried out using deionised water. Preferably, after waterwashing, the precipitated LDH is rinsed with the AMO-solvent.

According to the method of the invention, the collected and washed LDHis re-dispersed in the AMO-solvent so as to produce a slurry of the LDHin the solvent. The AMO-solvent is one that is miscible with water.Preferably, the AMO-solvent has a solvent polarity (P) in the range offrom 3.8 to 9. Solvent polarity (P) is defined based on experimentalsolubility data reported by Snyder and Kirkland (Snyder, L. R.;Kirkland, J. J. in Introduction to modern liquid chromatography, 2^(nd)ed.; John Wiley and Sons: New York, 1979; pp 248-250). Generally, anysuitable organic solvent may be used but preferably will be one selectedfrom acetone, acetonitrile, dimethylformamide, dimethyl sulphoxide,dioxane, ethanol, methanol, n-propanol, isopropanol or tetrahydrofuran.According to a particularly preferred embodiment, the organic solvent isacetone. The AMO-solvent comprised in the layered double hydroxide offormula (I) may be the same or different as the AMO-solvent used in thedispersing step.

The dispersion of LDH in the organic solvent is maintained preferablyfor at least three hours. It is preferred that the dispersion ismaintained under agitation and/or stirring. Stirring can be carried outusing a magnetic stirrer at a stirring speed which is preferably atleast 300 rpm and more preferably at least 1000 rpm. A propeller mixerhaving a peripheral speed of at least 0.5 m/s may, alternatively, beused. This ageing process is essential for obtaining an LDH having highsurface area. We have found that the surface area of the final productis dependent on the length of time the dispersion of the LDH in theorganic solvent is aged. Preferably, the slurry of LDH in the organicsolvent is aged for up to 96 hours, for instance for a period of from 1to 4 days. More preferably, the ageing period will be in the range offrom 1 to 3 days since we have found that the increase in surface areaof the LDH that occurs during ageing after the first 72 hours of ageingis not significant. Typically, the dispersion of LDH in the organicsolvent will be aged for from 48 to 72 hours. We have, further, foundthat it is beneficial to the final product if, after the dispersion ofLDH in organic solvent has been subjected to ageing, the organic solventis removed and the LDH is re-dispersed in fresh organic solvent. Whenthis re-dispersion of the LDH is carried out, the fresh dispersion ofthe LDH in fresh organic solvent may be maintained for up to 2 hours.

The aged dispersion of the LDH in organic solvent or, if the LDH hasbeen re-dispersed in fresh organic solvent, the re-dispersion is thensubjected to a procedure whereby the LDH may be recovered and dried. Wehave found that the specific surface area of the final dried productdepends on the drying procedure used.

According to one preferred embodiment, the step d) of recovering anddrying the LDH comprises filtering the LDH from the organic solvent andthen subjecting the collected LDH to drying. Drying may be carried outin an oven, with or without applied vacuum. Typically, oven drying willbe carried out at a relatively low temperature which will be dependenton the temperature at which the organic solvent evaporates. Preferably,the drying step, when the AMO solvent is acetone, will be carried out ata temperature in the range of room temperature (20° C.) to 60° C. In thepreferred embodiment according to which acetone is used as the organicsolvent, we have found that an oven temperature of about 60° C. may beused to dry the collected LDH. We have found that whereas a productdried overnight in an oven at 60° C. has a specific surface area ofabout 142 m²/g, a similar product dried overnight in an open vessel in avacuum oven has a specific surface area of 180 m²/g or greater.

According to a different preferred embodiment, the step d) of the methodcomprises passing the dispersion of LDH in the organic solvent to aspray drying apparatus and then spray drying the dispersion, typicallyusing an inert atmosphere such as nitrogen, so as to produce a spraydried LDH. We have found that by using a spray drying procedure toobtain a dry

LDH product from the dispersion in AMO-solvent, the final LDH has asignificantly increased surface area compared to an LDH product obtainedby filtering and then oven drying the filtered material. Furthermore, itappears from the results we have obtained that the specific surface areaof the final LDH obtained is dependent on the feed rate of thedispersion to the spray dryer and on the inlet and outlet temperaturesat the spray dryer. In the Examples provided, it is demonstrated that anLDH dispersion in acetone (aged for only one hour), spray dried using afeed rate in a range of 10-15 ml/min, an inlet temperature of 87° C. andan outlet temperature of 58° C., gives a final spray dried producthaving a specific surface area of about 316 m²/g whereas the samedispersion spray dried using a feed rate in a range of 20-25 ml/min, aninlet temperature of 95° C. and an outlet temperature of 57° C. gives afinal spray dried product having a specific surface area of about 333m²/g. Thus, according to a preferred embodiment, the LDH dispersion inthe AMO-solvent is fed into the spray dryer at a feed rate of at least12 ml/min, more preferably at least 18 ml/min and most preferably about24 ml/min.

In the formula (I) given for the LDH, M may be a single metal cation ora mixture of different metal cations. For example, when z is 2, M may beselected from Mg, Ca or Zn, or transition metal cations such as Fe, Ni,Co, Mn or Cu, and when z is 1, M may be Li. Preferred M are Mg, Zn, Fe,Ca, Ni, Co, Mn, Cu or a mixture of two or more of these.

M′ may be a single metal cation or a mixture of different metal cations.For example, when y=3, M′ may be selected from Al, Ga, Y, In, Fe, Co,Ni, Mn, Cr, Ti, V or La, and when y=4, M′ may be selected from Sn, Ti orZr or a mixture thereof. The preferred M′ is Al. The preferred value ofy is 3.

Preferably, z is 2 and M is Ca or Mg or Zn or Fe.

The preferred LDHs are Mg/Al, Ca/Al, Ni/Al, Cu/Al or Zn/Al.

Preferred values of x are 0.2 to 1, preferably 0.22 to 0.5, morepreferably 0.23 to 0.4.

The anion in the LDH may be any appropriate anion organic or inorganic,for example halide (e.g., chloride), inorganic oxyanions (e.g.X_(m)O_(n)(OH)_(p) ^(−q); m=1-5; n=2-10; p=0-4, q=1-5; X=B, C, N, S, P:e.g. carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate,nitrite, borate, nitrate, phosphate, sulphate), anionic surfactants(such as sodium dodecyl sulfate, fatty acid salts or sodium stearate),anionic chromophores, and/or anionic UV absorbers, for example4-hydroxy-3-10 methoxybenzoic acid, 2-hydroxy-4methoxybenzophenone-5-sulfonic acid (HMBA), 4-hydroxy-3-methoxy-cinnamicacid, p-aminobenzoic acid and/or urocanic acid.

According to one embodiment of the invention, the value of c is greaterthan zero. The following Examples demonstrate the preparation of LDHcompounds wherein c is 0.1.

The present invention further relates to a layered double hydroxide Aprepared by a method comprising

-   a) precipitating a layered double hydroxide B having the formula

[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(z))_(a/n) .bH₂O

-   -   wherein M and are different and each is a charged metal cation,        z=1 or 2; y=3 or 4; 0<x<0.9, b is 0 to 10, X is an anion, n is        the charge on the anion, and a=z(1−x)+xy−2; from a solution        containing the cations of the metals M and M′ and the anion        X^(n-).

-   b) ageing the layered double hydroxide precipitate obtained in    step a) in the original solution;

-   c) collecting, then washing the layered double hydroxide    precipitate;

-   d) dispersing the wet layered double hydroxide in an AMO-solvent so    as to produce a slurry of the layered double hydroxide in the    solvent;

-   e) maintaining the dispersion in step d); and

-   f) recovering and drying the layered double hydroxide A;

wherein the layered double hydroxide A has a specific surface area of atleast 125 m²/g.

Preferably, when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cdor a mixture of two or more of these, or when z is 1, M is Li.Preferably, when y is 3, M′ is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V,or La, or when y is 4, M is Sn, Ti or Zr or a mixture thereof.

According to a preferred embodiment, M′ is Al. The layered doublehydroxide A will especially be one selected from Zn/Al, Mg/Al, andCa/AI, Ni/Al, Cu/Al. Most preferably, the layered double hydroxide is anMg/AI layered double hydroxide.

Typically, X is an anion selected from at least one of halide, inorganicoxyanion, anionic surfactants, anionic chromophores, and anionic UVabsorbers. Examples of inorganic oxyanion include carbonate,bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate,nitrate, sulphate or phosphate or a mixture or two or more thereof.

The layered double hydroxide A of the invention has a specific surfacearea of at least 125 m²/g, preferably at least 240 m²/g.

The layered double hydroxide A of the invention preferably has a BETpore volume (N₂) of at least 0.5 cc/g, more preferably at least 1.0cc/g. The layered double hydroxide A of the invention preferably has aparticle size less than 150 μm, more preferably a particle size lessthan 30 μm.

When the layered double hydroxide A is dried by spray drying in step f),it typically has an agglomerated particle size less than 100 μm,preferably less than 30 μm.

According to a different aspect, the present invention provides aMg—Al—CO₃ layered double hydroxide having a specific surface area of atleast 300 m²/g, preferably at least 314 m²/g, more preferably at least330 m²/g.

The materials according to the invention are particularly suitable to beused for a large variety of applications, for instance as catalysts,catalyst supports, sorbents and coatings.

In the following Examples, the characterization methods used were:

X-Ray Diffraction (XRD)

XRD patterns were recorded on a PANalytical X'Pert Pro instrument inreflection mode with Cu Ka radiation. The accelerating voltage was setat 40 kV with 40 mA current (λ=1.542°) at 0.01° s⁻¹ from 1° to 70° witha slit size of ¼ degree.

Transmission Electron Microscopy (TEM)

TEM analysis was performed on JEOL 2100 microscope with an acceleratingvoltage of 400 kV. Samples were dispersed in ethanol with sonication andthen cast onto copper TEM grids coated with lacey carbon film.

Scanning Electron Microscopy (SEM)

SEM analyses were performed on a JEOL JSM 6100 scanning microscope withan accelerating voltage of 20 kV. Powder samples were spread on carbontape adhered to an SEM stage. Before observation, the samples weresputter coated with a thick Platinum layer to prevent charging and toimprove the image quality.

BET Specific Surface Areas

BET specific surface areas were measured from the N₂ adsorption anddesorption isotherms at 77 K collected from a Quantachrome Autosorb-6Bsurface area and pore size analyser. Before each measurement, LDHsamples were first degassed overnight at 110° C.

ThermoGravimetric Analysis

TGA's was carried out using a Perkin Elmer TGA7 ThermogravametricAnalyser. Approximately 10 mg of sample was heated in a platinum pan inthe furnace. Initially the temperature was held at 30° C. for 5 minutesand then was increased to 800° C. at a rate of 5° C. per minute. Thesample was held at 800° C. for five minutes. These data were used todetermine both the thermal stability and the H₂O and AMO solvent contentof the materials. Small variations in the H₂O and acetone content wasobserved on repeat measurements.

Further advantages and features of the subject-matter of the presentinvention can be taken from the following detailed description taking inconjunction with the drawing, in which:

FIG. 1: TEM images of Mg₃Al—CO₃ LDHs obtained from Example 1 beforedrying

FIG. 2: SEM images of Mg₃Al—CO₃ LDHs obtained from Example 1 after spraydrying

FIG. 3: XRD pattern of Mg₃Al—CO₃ LDHs obtained from Example 1 beforedrying a) only washed with water, b) dispersed in acetone for 48 hr.

FIG. 4: SEM images of Mg₃Al—CO₃ LDHs obtained from Example 2 afterdrying by oven

FIG. 5: SEM images of Mg₃Al—CO₃ LDHs obtained from Example 2 after spraydrying

FIG. 6: N₂-sorption isotherm of Mg₃Al—CO₃ LDHs obtained from Example 2after drying by oven

FIG. 7: N₂-sorption isotherm of Mg₃Al—CO₃ LDHs obtained from Example 2after spray drying

FIG. 8: SEM images of Mg₃Al—CO₃ LDHs obtained from Example 3 afterdrying by oven

FIG. 9: SEM images of Mg₃Al—CO₃ LDHs obtained from Example 3 after spraydrying

FIG. 10: N₂-sorption isotherm of Mg₃Al—SO₄ LDHs obtained from Example 9after drying in vacuum oven

FIG. 11: TEM images of Mg₃Al—CO₃ LDHs obtained from Example 10 beforedrying (A) water washed (B) 1000 mL of rinsed acetone

FIG. 12: N₂-sorption isotherm of Mg₃Al—CO₃ LDHs obtained from Example 10rinsed with acetone of 100 mL, 300 mL and 1000 mL.

FIG. 13: BET surface area and LDH layers of of Mg₃Al—CO₃ LDHs obtainedfrom Example 10 rinsed with different amount of acetone.

FIG. 14: BET surface area and LDH layers of of Mg₃Al—CO₃ LDHs obtainedfrom Example 10 dispersed in acetone for different dispersion time.

FIG. 15: BET surface area and LDH layers of of Mg₃Al—CO₃ LDHs obtainedfrom Example 10 dispersed in acetone for different dispersion cycles.

FIG. 16: N₂-sorption isotherm of Mg₃Al—CO₃ LDHs obtained from Example 11dispersed in acetone for 1 h, 2 h and 4 h.

FIG. 17: BET surface area and LDH layers of of Mg₃Al—CO₃ LDHs obtainedfrom Example 11 dispersed in acetone for different dispersion time.

FIG. 18: BET surface area and LDH layers of of Mg₃Al—CO₃ LDHs obtainedfrom Example 11 dispersed in acetone for different dispersion cycles.

EXAMPLES Example 1

A metal precursor solution was prepared by dissolving 9.6 g ofMg(NO₃)₂.6H₂O and 4.68 g of Al(NO₃)₃.9H₂O in 50 mL deionized water. Abase solution was prepared by dissolving 4 g of NaOH and 2.65 g ofNa₂CO₃ in 200 mL of deionized water. The metal precursor solution wasadded quickly into base solution under visciously stirring. After 30min, the resulting slurry was collected by filtration and washedthoroughly with water and acetone successively. The washed filter cakewas re-dispersed into acetone (200 mL) with stirring at 60° C. After 48h, the acetone in the suspension was removed and fresh acetone (200 mL)was introduced. The obtained new suspension was stirred at roomtemperature for 2 h. The suspension was filtered to collect the LDHsolid which was then washed thoroughly with acetone. The final product[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1 (acetone)=(Mg₃Al—CO₃LDH) was dried in an oven at 60° C. overnight.

The BET surface area and pore volume of the resulting Mg³⁻Al—CO₃ LDH areshown in Table 1. The morphology of the Mg³⁻Al—CO₃ before drying ispresented in FIG. 1. The morphology of the Mg₃—Al—CO₃ LDH after dryingby spray dryer are presented in SEM images in FIG. 2. The purity of theobtained Mg₃—Al—CO₃ LDH was examined by X-Ray Diffraction as shown inFIG. 3.

TABLE 1 BET surface area and pore volume of Mg₃—Al—CO₃ LDHs obtainedfrom Example 1. Range of feed rate BET Total pore Drying to spray dryersurface volume Methods (mL/min) area (m²/g) (cc/g) Oven, 65° C. — 1410.71 (overnight) Filter + vacuum — 180 0.92 Spray dryer* 20-25 248 1.99*all the samples dried using spray dryer (the same as below) wereconducted in the same conditions, which is using the same outlettemperature of 55° C.

Example 2

[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.125).0.0.1H₂O.0.1(acetone)=Mg₃Al—CO₃LDH was synthesized by adding 200 mL Mg(NO₃)₂.6H₂O (0.15 mol) andAl(NO₃)₃.9H₂O (0.05 mol) solution drop-wise into a 200 ml Na₂CO₃ (0.10mol) solution with a drop rate in the range of 0.1-3.5{mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH of the precipitationsolution was controlled at 10 using a NaOH solution (4M), the resultingslurry was left for 16 hrs at room temperature. The obtained LDH slurrywas filtered and washed with deionized water until a pH=7 was obtainedand then the filtered solid was washed with acetone 500 ml throughsuction filter funnel. The “wet cake” was re-dispersed in 1000 mlacetone for 1 hr.

Half of the LDH produced, suspended in acetone, was dried by oven at 65°C. and the other half was dried by spray drying in a N₂ atmosphere. TheBET surface area and pore volume of the resulting[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.125).0.1H₂O.0.1(acetone)=(Mg₃Al—CO₃LDH) Mg₃—Al—CO₃ LDH are shown in Table 2. The morphology of Mg₃—Al—CO₃LDH after drying by oven and spray dryer are comparatively presented inSEM images in FIGS. 4 and 5, respectively. N₂-sorption isotherm ofMg₃Al—CO₃ LDHs obtained after drying by oven and spray dryer were shownin FIGS. 6 and 7, respectively.

TABLE 2 BET surface area and pore volume of Mg₃—Al—CO₃ LDHs obtainedfrom Example 2. Range of feed rate Total pore Drying to spray dryer BETsurface volume Methods (mL/min) area (m²/g) (cc/g) Oven, 65° C. — 1540.88 (overnight) Spray dryer 10-15 316 1.37 Spray dryer 15-20 330 1.36Spray dryer 20-25 333 1.45 Spray dryer 25-30 314 1.19

Example 3

[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.125).0.1H₂O.0.1 (acetone)=Mg₃Al—CO₃LDH was synthesized by adding 200 mL Mg(NO₃)₂.6H₂O (0.15 mol) andAl(NO₃)₃.9H₂O (0.05 mol) solution drop-wise into a 200 mL Na₂CO₃ (0.10mol) solution with the drop rate in the range of 0.1-3.5{mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH of the precipitationsolution was controlled at lousing a NaOH solution (4 M). After 30 min.of ageing in original solution, the resulting slurry was filtered andwashed with deionized water until a pH=7 was obtained. The filteredslurry was washed with acetone 500 mL through suction filter funnelfollowed by dispersion in 500 mL of acetone. After 16 hrs of stirring,the suspension was filtered and introduced fresh acetone (1000 mL) foranother 1 hr of stirring. The half of LDH suspended in acetone was driedby oven at 65° C. and the other half was dried by spray drying in a N₂atmosphere. The BET surface area and pore volume results of theresulting Mg₃—Al—CO₃ LDH are shown below in Table 3. The morphology ofMg₃—Al—CO₃ LDH after drying by oven and spray dryer are comparativelypresented in SEM images in FIGS. 8 and 9, respectively.

TABLE 3 BET surface area and pore volume of Mg₃—Al—CO₃ LDHs obtainedfrom Example 3. Range of feed rate Total pore Drying to spray dryer BETsurface volume Methods (mL/min) area (m²/g) (cc/g) Oven, 65° C. — 2781.10 (overnight) Spray dryer 25-30 326 1.25

Example 4

[Ni_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.42H₂O.0.13(acetone)=Ni_(0.3)Mg_(2.7)Al—CO₃LDH was synthesized by adding 700 mL Ni(NO₃)₂.6H₂O (0.0525 mol) andMg(NO₃)₂.6H₂O (0.4725 mol) and Al(NO₃)₃.9H₂O (0.175 mol) solutiondrop-wise into a 700 ml Na₂CO₃ (0.35 mol) solution with a drop rate inthe range of 0.1-3.5 {mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH ofthe precipitation solution was controlled at 10 using a NaOH solution(4M), the resulting slurry was left for 16 hrs at room temperature. Theobtained LDH slurry was filtered and washed with deionized water until apH=7 was obtained and then the filtered solid was washed with acetone3000 ml through suction filter funnel. The “wet cake” was re-dispersedin 1750 ml acetone for 1 hr.

Half of the LDH produced, suspended in acetone, was dried by oven at 65°C. and the other half was dried by spray drying in a N₂ atmosphere. TheBET surface area and pore volume of the resulting[Ni_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.42H₂O.0.13(acetone)=(Ni_(0.3)Mg_(2.7)Al—CO₃ LDH)Ni_(0.3)—Mg_(2.7)—Al—CO₃ LDH are shown in Table 4.

TABLE 4 BET surface area and pore volume of Ni_(0.3)—Mg_(2.7)—Al—CO₃LDHs obtained from Example 4. Range of feed rate Total pore Drying tospray dryer BET surface volume Methods (mL/min) area (m²/g) (cc/g) Oven,65° C. — 177 0.65 (overnight) Spray dryer 20-25 317 0.84

Example 5

[Cu_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=Cu_(0.3)Mg_(2.7)Al—CO₃LDH was synthesized by adding 700 mL Cu(NO₃)₂.6H₂O (0.0525 mol) andMg(NO₃)₂.6H₂O (0.4725 mol) and Al(NO₃)₃.9H₂O (0.175 mol) solutiondrop-wise into a 700 ml Na₂CO₃ (0.35 mol) solution with a drop rate inthe range of 0.1-3.5 {mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH ofthe precipitation solution was controlled at 10 using a NaOH solution(4M), the resulting slurry was left for 16 hrs at room temperature. Theobtained LDH slurry was filtered and washed with deionized water until apH=7 was obtained and then the filtered solid was washed with acetone3000 ml through suction filter funnel. The “wet cake” was re-dispersedin 1750 ml acetone for 1 hr.

The LDH produced, suspended in acetone, was dried by spray drying in aN₂ atmosphere. The BET surface area and pore volume of the resulting[Cu_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=(Cu_(0.3)Mg_(2.7)Al—CO₃LDH) Cu_(0.3)—Mg_(2.7)—Al—CO₃ LDH are shown in Table 5.

TABLE 5 BET surface area and pore volume of Cu_(0.3)—Mg_(2.7)—Al—CO₃LDHs obtained from Example 5. Range of feed rate Total pore Drying tospray dryer BET surface volume Methods (mL/min) area (m²/g) (cc/g) Spraydryer 20-25 252 1.00

Example 6

[Co_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=Co_(0.3)Mg_(2.7)Al—CO₃LDH was synthesized by adding 700 mL Co(NO₃)₂.6H₂O (0.0525 mol) andMg(NO₃)₂.6H₂O (0.4725 mol) and Al(NO₃)₃.9H₂O (0.175 mol) solutiondrop-wise into a 700 ml Na₂CO₃ (0.35 mol) solution with a drop rate inthe range of 0.1-3.5 {mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH ofthe precipitation solution was controlled at 10 using a NaOH solution(4M), the resulting slurry was left for 16 hrs at room temperature. Theobtained LDH slurry was filtered and washed with deionized water until apH=7 was obtained and then the filtered solid was washed with acetone3000 ml through suction filter funnel. The “wet cake” was re-dispersedin 1750 ml acetone for 1 hr.

The LDH produced, suspended in acetone, was dried by spray drying in aN₂ atmosphere. The BET surface area and pore volume of the resulting[Co_(0.075)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=(Co_(0.3)Mg_(2.7)Al—CO₃ LDH)Co_(0.3)—Mg_(2.7)—Al—CO₃ LDH are shown in Table 6.

TABLE 6 BET surface area and pore volume of Co_(0.3)—Mg_(2.7)—Al—CO₃LDHs obtained from Example 6. Range of feed rate Total pore Drying tospray dryer BET surface volume Methods (mL/min) area (m²/g) (cc/g) Spraydryer 20-25 256 1.06

Example 7

[Cu_(0.0075)Ni_(0.0675)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=Cu_(0.03)Ni_(0.27)Mg_(2.7)Al—CO₃LDH was synthesized by adding 700 mL Cu(NO₃)₂.6H₂O (0.00525 mol) andNi(NO₃)₂.6H₂O (0.04725 mol) and Mg(NO₃)₂.6H₂O (0.4725 mol) andAl(NO₃)₃.9H₂O (0.175 mol) solution drop-wise into a 700 ml Na₂CO₃ (0.35mol) solution with a drop rate in the range of 0.1-3.5{mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH of the precipitationsolution was controlled at 10 using a NaOH solution (4M), the resultingslurry was left for 16 hrs at room temperature. The obtained LDH slurrywas filtered and washed with deionized water until a pH=7 was obtainedand then the filtered solid was washed with acetone 3000 ml throughsuction filter funnel. The “wet cake” was re-dispersed in 1750 mlacetone for 1 hr.

The LDH produced, suspended in acetone, was dried by spray drying in aN₂ atmosphere. The BET surface area and pore volume of the resulting[Cu_(0.0075)Ni_(0.0675)Mg_(0.675)Al_(0.25)(OH)₂](CO₃)_(0.125).0.4H₂O.0.1(acetone)=(Cu_(0.03)Ni_(0.27)Mg_(2.7)Al—CO₃LDH) Cu_(0.03)—Ni_(0.27)—Mg_(2.7)—Al—CO₃ LDH are shown in Table 7.

TABLE 7 BET surface area and pore volume ofCu_(0.03)—Ni_(0.27)—Mg_(2.7)—Al—CO₃ LDHs obtained from Example 7. Rangeof feed rate Total pore Drying to spray dryer BET surface volume Methods(mL/min) area (m²/g) (cc/g) Spray dryer 20-25 197 0.74

Example 8

[Mg_(0.75)Al_(0.25)(OH)₂](NO₃)_(0.25).0.32H₂O.0.12(acetone)=Mg₃Al—NO₃LDH was synthesized by adding 700 mL Mg(NO₃)₂.6H₂O (0.525 mol) andAl(NO₃)₃.9H₂O (0.175 mol) solution drop-wise into a 700 ml NaNO₃ (0.35mol) solution with a drop rate in the range of 0.1-3.5{mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH of the precipitationsolution was controlled at 10 using a NaOH solution (4M), the resultingslurry was left for 16 hrs at room temperature. The obtained LDH slurrywas filtered and washed with deionized water until a pH=7 was obtainedand then the filtered solid was washed with acetone 3000 ml throughsuction filter funnel. The “wet cake” was re-dispersed in 1750 mlacetone for 1 hr.

The LDH produced, suspended in acetone, was dried by spray drying in aN₂ atmosphere. The BET surface area and pore volume of the resulting[Mg_(0.75)Al_(0.25)(OH)₂](NO₃)_(0.25).0.32H₂O.0.12(acetone)=(Mg₃Al—NO₃LDH) Mg₃Al—NO₃ LDH are shown in Table 8.

TABLE 8 BET surface area and pore volume of Mg₃Al—NO₃ LDHs obtained fromExample 8. Range of feed rate Total pore Drying to spray dryer BETsurface volume Methods (mL/min) area (m²/g) (cc/g) Spray dryer 20-25 2120.85

Example 9

[Mg_(0.75)Al_(0.25)(OH)₂](SO₄)_(0.25).0.55H₂O.0.13(acetone)=Mg₃Al—SO₄LDH was synthesized by adding 20 mL Mg(SO₄)₂ (0.0375 mol) andAl(SO₄)₃.16H₂O (0.0125 mol) solution quickly into a 50 ml solutioncontaining 0.025 mol of Na₂SO₄ and 0.075 mol of NaOH. The resultingslurry was left for 30 min at room temperature. The obtained LDH slurrywas filtered and washed with deionized water until a pH=7 was obtainedand then the filtered solid was washed with acetone 500 mL throughsuction filter funnel. The “wet cake” was re-dispersed in 300 mL acetonefor 2 hrs. The slurry was filtered and redispersed in 300 mL acetone for2 hrs.

The LDH produced was filtrated and dried in vacuum oven for 16 hrs. TheBET surface area and pore volume of the resulting[Mg_(0.75)Al_(0.25)(OH)₂](SO₄)_(0.25).0.55H₂O.0.13(acetone)=(Mg₃Al—SO₄LDH) Mg₃Al—SO₄ LDH are shown in Table 9. N₂-sorption isotherm ofMg₃Al—SO₄ LDHs after drying in vacuum oven can be shown in FIG. 10.

TABLE 9 BET surface area and pore volume of Mg₃Al—SO₄ LDHs obtained fromExample 9. Range of feed rate Total pore Drying to spray dryer BETsurface volume Methods (mL/min) area (m²/g) (cc/g) Vacuum oven — 1800.93 (Room temperature)

Example 10

[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.26).0.1H₂O.0.1 (acetone)=Mg₃Al—CO₃ LDHwas synthesized by adding the metal precursor solution (20 mL) of 1.875M Mg(NO₃)₂.6H₂O and 0.625 M Al(NO₃)₃.9H₂O into the 50 mL of 0.5 M Na₂CO₃solution with a drop rate in the range of 0.1-3.5 mol{mol(M^(z+)+M^(y+))}/{mol(anion)*min}. The pH value was kept at ca. 10.0by dropwise addition of a 4.0 M NaOH solution. After 30 min withstirring at room temperature, the slurry was washed with DI water untilthe pH was close to 7 following by being rinsed with certain amount ofacetone (step 1: rinsed acetone). The obtained LDH wet cake wasdispersed in acetone (300 mL) and stirred at room temperature forcertain time (step 2: dispersion time). Then the LDH was filtered andre-dispersed into flesh acetone (300 mL) for dispersion cycle study(step 3: dispersion cycle) or dried in vacuum oven for 16 hrs. The BETsurface area and pore volume of the resulting Mg₃Al—CO₃ LDH in each stepare shown in Tables 10-12. The morphology of wet Mg₃—Al—CO₃ LDH afterwater washing and 1000 mL of rinsed acetone are comparatively presentedin TEM images in FIG. 11. N₂-sorption isotherm of Mg₃Al—CO₃ LDHsobtained after rinsing with different volumes of acetone were shown inFIG. 12. The surface area and LDH layers of Mg₃Al—CO₃ LDHs after eachstep were shown in FIG. 13-15.

TABLE 10 BET surface area and pore volume of Mg₃Al—CO₃ LDHs obtainedfrom Step 1 (Rinsed acetone) in Example 10. Drying Rinsed acetone BETsurface Total pore Methods (mL) area (m²/g) volume (cc/g) Vacuum oven 00.07 0.002 (Room 300 163 0.79 temperature) 500 229 0.79 1000 339 1.34

TABLE 11 BET surface area and pore volume of Mg₃Al—CO₃ LDHs obtainedfrom Step 2 (Dispersion time) in Example 10 (Rinsed acetone: 500 mL).Drying Dispersion BET surface Total pore Methods time (h) area (m²/g)volume (cc/g) Vacuum oven 0 0.07 0.002 (Room 1 363 1.18 temperature) 2352 1.25 3 364 1.17

TABLE 12 BET surface area and pore volume of Mg₃Al—CO₃ LDHs obtainedfrom Step 3 (Dispersion cycle) in Example 10 (Rinsed acetone: 500 mL,dispersion time: 1 h, 300 mL). Drying Dispersion BET surface Total poreMethods cycle area (m²/g) volume (cc/g) Vacuum oven 0 0.07 0.002 (Room 1363 1.18 temperature) 2 204 0.93 3 269 1.13

Example 11

[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.25).0.4H₂O.0.1(acetone) Mg₃Al—CO₃ LDHwas synthesized by adding the metal precursor solution (20 mL) of 1.875M Mg(NO₃)₂.6H₂O and 0.625 M Al(NO₃)₃.9H₂O quickly into the 50 mL of 0.5M Na₂CO₃ solution. The pH value was kept at ca. 10.0 by dropwiseaddition of a 4.0 M NaOH solution. After 30 min with stirring at roomtemperature, the slurry was washed with DI water until the pH was closeto 7 following by being rinsed with certain amount of acetone (step 1:rinsed acetone). The obtained LDH wet cake was dispersed in acetone (300mL) and stirred at room temperature for certain time (step 2: dispersiontime). Then the LDH was filtered and re-dispersed into flesh acetone(300 mL) for dispersion cycle study (step 3: dispersion cycle) or driedin vacuum oven for 16 hrs.

The BET surface area and pore volume of the resulting Mg₃Al—CO₃ LDH ineach step are shown in Table 13-14. N₂-sorption isotherm of Mg₃Al—CO₃LDHs obtained after rinsing with different dispersion time of acetonewere shown in FIG. 16. The surface area and LDH layers of Mg₃Al—CO₃ LDHsafter Step 2 and Step 3 were shown in FIG. 17-18.

TABLE 13 BET surface area and pore volume of Mg₃Al—CO₃ LDHs obtainedfrom Step 2 (Dispersion time) in Example 11 (Rinsed acetone: 500 mL).Drying Dispersion BET surface Total pore volume Methods time (h) area(m²/g) (cc/g) Vacuum oven 0 0.08 0.00 (Room 1 90 0.55 temperature) 2 1400.75 4 220 1.07 12 232 0.86

TABLE 14 BET surface area and pore volume of Mg₃Al—CO₃ LDHs obtainedfrom Step 3 (Dispersion cycle) in Example 11 (Rinsed acetone: 500 mL,dispersion time: 1 h, 300 mL). Drying Dispersion BET surface Total porevolume Methods cycle area (m²/g) (cc/g) Vacuum oven 0 0.08 0.00 (Room 1220 1.07 temperature) 2 269 0.93 3 238 1.13

1. A method of preparing a layered double hydroxide having a specificsurface area of at least 125 m²/g and having the formula:[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(n-))_(a/n) ⁺bH₂O.c(AMO-solvent)  (I) wherein M and M′ are different and each is acharged metal cation (and must be present), z=1 or 2; y=3 or 4, 0<x<0.9,b is 0 to 10, c=0 to 10, X is an anion, n is the charge on the anion,a=z(1−x)+xy−2; and AMO-solvent is an aqueous miscible organic solvent,which method comprises a) precipitating a layered double hydroxidehaving the formula[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(n-))_(a/n) ⁺ bH₂O wherein M,M′, z, y, x, a, b and X are as defined above from a solution containingthe cations of the metals M and M′ and the anion X^(n-); b) ageing thelayered double hydroxide precipitate obtained in step a) in the originalsolution; c) collecting, then washing the layered double hydroxideprecipitate; d) dispersing the wet layered double hydroxide in an AMOsolvent so as to produce a slurry of the layered double hydroxide in thesolvent; e) maintaining the dispersion obtained in step d); and f)recovering and drying the layered double hydroxide.
 2. A methodaccording to claim 1, wherein the AMO: solvent is an aqueous miscibleorganic solvent having a solvent polarity (P) in the range 3.8 to
 9. 3.A method according to claim 1, wherein, in formula (I), when z is 2, Mis Mg, Zn, Fe, Ca, Sn Ni, Cu, Co, Mn or Cd or a mixture of two or moreof these, or when z is 1, M is Li.
 4. A method according to claim 1,wherein, in formula (I), when y is 3, M′ is Al, Ga, Y, In, Fe, Co, Ni,Mn, Cr, Ti, V, or La, or when y is 4, M′ is Sn, Ti or Zr or a mixturethereof.
 5. A method according to claim 4, wherein M′ is Al.
 6. A methodaccording to claim 5, wherein the layered double hydroxide is selectedfrom Zn/Al, Mg/Al, and Ca/Al, Ni/Al, Cu/Al.
 7. A method according toclaim 6, wherein the layered double hydroxide is an Mg/Al layered doublehydroxide.
 8. A method according to claim 1, wherein X is an anionselected from at least one of halide, inorganic oxyanion, anionicsurfactants, anionic chromophores, and anionic UV absorbers.
 9. A methodaccording to claim 8, wherein the inorganic oxyanion is carbonate,bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate,nitrate, sulphate or phosphate or a mixture of two or more thereof. 10.A method according to claim 1, wherein in step a) the layered doublehydroxide precipitate is formed by introducing metal (M^(z+)+M′^(y+))solution to the anion (X^(n-)) solution with a drop rate in the range of0.1 to 3.5 {mol(M^(z+)+M^(y+))}/{mol(anion)*min}.
 11. A method accordingto claim 1, wherein in step a) the layered double hydroxide isprecipitated from the cation and anion containing solution which eitheradditionally contains NaOH or to which NaOH solution is added separatelyto adjust pH of solution to a predetermined value.
 12. A methodaccording to claim 1, wherein in step b) the layered double hydroxideprecipitate is aged in the original solution for less than 24 hours. 13.A method according to claim 1, wherein in step c) the layered doublehydroxide is collected by filtration and washed with water until the pHof the washing is substantially neutral and then rinsed withAMO-solvent.
 14. A method according to claim 1, wherein in step d) thewet layered double hydroxide obtained in step c) is dispersed andmaintained in AMO-solvent under stirring.
 15. A method according toclaim 1, wherein in step e) the dispersion obtained in step d) ismaintained for up to 96 hours.
 16. A method according to claim 1,wherein after step e) the layered double hydroxide is collected as wetform and is dispersed in a fresh volume of the AMO solvent and thedispersion is maintained for at least two hours.
 17. A method accordingto claim 1, wherein in step f), the layered double hydroxide isrecovered by filtration and the recovered layered double hydroxide isdried in an oven or by a spray dryer.
 18. (canceled)
 19. A layereddouble hydroxide A having a specific surface area of at least 125 m²/gand having the formula:[M^(z+) _(1-x)M′^(y+) _(x)(OH)₂]^(a+)(X^(n-))_(a/n) ⁺bH₂O.c(AMO-solvent)  (I) wherein M and M′ are different and each is acharged metal cation (and must be present), z=1 or 2; y=3 or 4, 0<x<0.9,b is 0 to 10, c=0 to 10, X is an anion, n is the charge on the anion,a=z(1−x)+xy−2; and AMO-solvent is an aqueous miscible organic solvent.20. A layered double hydroxide A according to claim 19, wherein thelayered double hydroxide A has a specific surface area of at least 240m²/g.
 21. (canceled)
 22. A layered double hydroxide A according to claim21, wherein the layered double hydroxide A has a BET pore volume (N₂) ofat least 1.0 cc/g.
 23. A layered double hydroxide A according to claim19, wherein the layered double hydroxide A has a particle size less than150 μm.
 24. A layered double hydroxide A according to claim 23, whereinthe layered double hydroxide A has a particle size less than 30 μm. 25.(canceled)
 26. A layered double hydroxide A according to claim 25,wherein the layered double hydroxide A is dried by spray drying and hasan agglomerated particle size less than 30 μm.